1. Field of the Invention
Embodiments of the subject matter disclosed herein generally relate to methods and systems and, more particularly, to mechanisms and techniques for recovering natural gas liquids (NGL).
2. Description of the Prior Art
During the past years, with the increase in price of gas and oil fuels, many aspects of the extraction, transportation and processing of the gas and oil have received increased attention. There is an interest in making the existing machines and processes more efficient and reliable and also for reducing the waste associated with many aspects of oil and gas industry.
FIG. 1 shows part of the infrastructure used for extracting, transporting and processing the oil and/or gas, simply called from now on the product. Such a system 10 includes at least an extraction facility 12 that may be on shore (as shown in the figure) or off-shore (not shown). Such extraction facility 12 may be a rig or other known devices that drill underground for reaching a reservoir 14 of oil and/or gas. Once the product is brought to the surface 16, it may be stored in a storage facility 18. As most of the times the extraction facility is located far from a processing facility, the product needs to be transported, some times over thousands of miles. Thus, a pumping facility 20 may be provided next to the storage facility 18. The pumping facility 20 may include a generic pumping and pumping systems to increase the pressure of the product before entering an inlet 22 of a transportation pipeline 24. The transportation pipeline may be distributed above ground (not shown) and underground as shown in FIG. 1. As the pressure of the product decreases while moving along the pipeline 24, pumping stations 26 are provided along the pipeline 24 for boosting the pressure of the product.
Typically, a pumping station includes at least a pump if the product is a liquid or at least a compressor if the product is a gas. For simplicity, it is assumed in the following that the product is a gas. Thus, a compression station 26 includes one or more compressors and a gas turbine that powers the compressor. The gas turbine is configured to divert part of the product from the pipeline 24 as fuel. At the end of the journey, the product arrives at the processing facility 28 where the product is separated in various components 30. These components are then sold to the appropriate customers.
One example of a product is the raw natural gas. Raw natural gas consists primarily of methane (CH4), the shortest and lightest hydrocarbon molecule, as well as various amounts of heavier hydrocarbon gases such as ethane (C2H6), propane (C2H8), normal butane (n-C4H10), isobutane (i-C4H10), pentanes and even higher molecular weight hydrocarbons. Based on the number of carbons, these components are sometimes classified as C, C1, C2, C3, etc. The raw gas also contains various amounts of acid gases such as carbon dioxide (CO2), hydrogen sulfide (H2S) and mercaptans such as methanethiol (CH3SH) and ethanethiol (C2H5SH).
When processed into finished by-products, these heavier hydrocarbons are collectively referred to as NGL. The extraction of the NGL often involves a turbo-expander and a low-temperature distillation column (called a demethanizer). The inlet gas to the demethanizer may be cooled in a heat exchanger which partially condenses the inlet gas. The resultant gas-liquid mixture is then separated in a separator into a gas stream and a liquid stream. Typical processing facilities are complex and include demethanizer units, multiple separators, separated refrigeration loops, glycol injecting units, etc.
However, there are situations when at least parts of the above noted system 10 in a gas station/pipeline are desired to have a simplified, structure or to provide fuel at a given specification or to prevent the gas turbines to burn NGLs. Regarding the simplified structure, it is noted the complexity of the processing facility 28, which requires multiple separators, at least a demethanizer unit, and other components makes the footprint of the facility large and also makes the facility prone to failures. Also, it is noted that the compression stations 26 may include compressors which are driven by gas turbines which need fuel with certain specifications for their functioning. As the compression stations 26 transport natural gas, many of the compression stations 26 use part of the natural gas as fuel. However, the transported natural gas could not be appropriate for being burned in a gas turbine (might not meet those specifications). Thus, an amount of pollution is increased by feeding the gas turbine with untreated natural gas. In addition, the amount of the NGLs in the transported natural gas is reduced due to the fact that the NGL is used as fuel within natural gas/together with methane.
Accordingly, it would be desirable to provide systems and methods that avoid the afore-described problems and drawbacks.